[PATCH V3] configure.ac: Fallback to older detection code if pkg-config can't find expat

[Bill Spitzak]

Okay after some searching I found a working method of compiling expat, 
and have sent a patch to update the Ubuntu12.04 build instructions, and 
this patch should be ignored.

On 02/03/2015 02:29 PM, Peter Hutterer wrote:
> On Tue, Feb 03, 2015 at 02:10:32PM -0800, Bill Spitzak wrote:
>>
>>
>> On 02/03/2015 01:50 PM, Peter Hutterer wrote:
>>> On Tue, Feb 03, 2015 at 12:33:35PM -0800, Bill Spitzak wrote:
>>>> This paritally reverts commit a4afd90f9f0c27ed5f3f313b915c260673f8be34.
>>>>
>>>> On older expat versions (ie the one on Ubuntu 12.04) there is no pkg-config
>>>> file, so fall back to a test for the header and library.
>>>
>>> hmm, this is the first time I read this paragraph: 12.04 is almost 2 years
>>> old now, are there any more recent examples that need this patch? If not,
>>> I'd recommend going with "install newer expat in your prefix" than
>>> adding build system workarounds.
>>
>> Any idea where it is? I can find a cvs repository on SourceForge. Would
>> rather not add yet another dependency on using cvs! Is it on git somewhere
>> or is this cvs the official version?
>>
>> I could also just place a fake pkg-config file in the install directory.
>>
>> Both of these would require updating the Ubuntu build directions page.
>>
>> Both by previous employers are frozen at Ubuntu 12.04, I don't think this is
>> uncommon. The earlier one had finally updated from a 5 year old system from
>> SUSE.
>
> http://expat.sourceforge.net indicates the CVS repository is the upstream
> repo. Also, it looks like the pkgconfig file was added in 2007, talk about a
> slow release cycle...
>
>>> that looks correct, but the ,, almost caught me and the nesting is a bit
>>> hard to read. How about:
>>>
>>> PKG_CHECK_MODULES(EXPAT, [expat], HAVE_EXPAT="yes", HAVE_EXPAT="no")
>>> if test x$HAVE_EXPAT = "xno"; then
>>>          AC_CHECK_HEADERS
>>>          ...
>>>          AC_SEARCH_LIBS
>>>          ...
>>>          AC_SUBST # I think you should have it explicitly here
>>> fi
>>
>> I find that much harder to read because of the unreadability of binary tests
>> in M4 and reliance on an intermediate variable. Also it makes it harder to
>> remove the fallback code in the future. But I think I can get rid of the
>> double commas, though they are used elsewhere.
>
> the thing here is that this is what a lot of projects use, so most
> developers are used to exactly that control sequence. Which makes it safer
> to use than any other solution where one actually has to switch the brain on
> to parse what it's doing ;)
>
> Note that weston already uses this sequence (in slight variations) for rdp,
> with-cairo, wedp, libva, libjpeg, etc.
> So please go with a simple solution that's already in use, it makes life a
> lot easier for everyone else. configure scripts should not the be a
> target for optimization, readability is king here.
>
> Cheers,
>     Peter
>